Gelled ammonium nitrate-nitromethane explosive composition



United States Patent Oil 3,377,217 GELLED AMMONIUM NITRATE-NITROMETHANEEXPLOSIVE COMPOSITION James W. Francis, Marion, Ill., assignor toCommercial Solvents Corporation, New York, N.Y., a corporation ofMaryland No Drawing. Filed Dec. 12, 1966, Ser. No.

6 Claims. (Cl. 149-50) ABSTRACT OF THE DISCLOSURE This invention relatesto explosive compositions containing ammonium nitrate and nitromethane.In a particular aspect this invention relates tonon-cap-sensitiveexplosive compositions, in gelled form having high rates of detonation.In a further aspect this invention relates to non-cap-sensitiveexplosive compositions'in' gelled form having high rates of detonationuseful in the seismic exploration for oil and natural gas found beneaththe ocean floor.

Explosives are used in the seismic exploration for oil and gas depositsfound beneath the'ocean fioor. Energy from shock waves produced by thedetonation of expIosives beneath the surface of the water travelsdownward to beneath the ocean floor and is then partially reflectedupward. The energy returning to the surface is picked up by a receivingapparatus known as a geophone which in turn transmits the receivedimpulses to amplifying and recording devices. Interpretation of therecorded information permits the skilled geophysicist to determinegeological structures where oil and natural gas are likely to haveaccumulated.

Explosive compositions used in marine seismic petroleum explorationdesirably have high rates of detonation. Because of the stringent safetyrequirements in major ports regarding the loading of explosives on oceangoing vessels, such explosives must also be non-cap-sensitive; that is,incapable of detonation by a single No. '8 electric blasting cap.

Explosive compositions in gelled form comprising ammonium nitrate,nitroparaflins such as nitromethane, nitroethane and nitropropane and agelling agent for the nitroparaflin are known to the art and have a widevariety of applications. Prior explosive compositions containingammonium nitrate and nitroparalfins in gelled form have not beensuitable for use in marine seismic exploration because of failure of thecompositions to meet the requirements outlined above.

It is an object of the present invention to provide noncap-sensitiveexplosive compositions in gelled form having high rates of detonationcontaining ammonium nitrate and nitromethane.

It is a further object of the present invention to providenon-cap-sensitive explosive compositions in gelled form having highrates of detonation useful in marine seismic exploration for oil andnatural gas.

Other objects and advantages of the present invention ice will beapparent from the specification and appended claims.

The present invention resides in the discovery that noncap-sensitiveexplosive compositions having high rates of detonation are prepared byforming an intimate admixture of ammonium nitrate of particle sizesufliciently small to substantially completely pass through a 10 meshscreen with not more than 22% passing through a 200 mesh screen,nitromethane, and a gelling agent for the nitromethane wherein theweight ratio of ammonium nitrate to nitromethane is in the range of fromabout 65:35 to about 45:55.

In the present application the terms rate of detonation and detonationrate are used interchangeably with the term detonation velocity. Therate of detonation of an explosive is the rate at which the detonationfront passes through the explosive material. Detonation rate istypically expressed in feet per second. For the purpose of the presentinvention high detonation rates are generally considered to be in excessof 12,000 feet per second. The compositions of the present inventionhave detonation rates in excess of 18,000 feet per second withdetonation rates of in excess of 20,000 feet per second being reasonablycommon in freshly prepared material; that is, material prepared withinthe most recent 24-hour period.

Any suitable gelling agent for thickening or gelling the normally liquidnitromethane may be employed in the compositions of the presentinvention. Examples of such gelling agents include nitrocellulose, ethylcellulose, cellulose acetate, cellulose acetate butyrate,polyoxyethylene having molecular weights in the range of from about onehundred thousand to about five million and the like. Because of theexcellent results obtained therewith, nitrocellulose is preferred as thegelling agent.

The amount of gelling agent suitable for use in the explosivecompositions of the present invention will vary depending principally onthe particular gelling agent employed and on the viscosity desired foreach particular composition. Typically, amounts in the range of fromabout 2 to about 15% by weight of gelling agent based on the weight ofthe nitromethane are employed. Preferred amounts are in the range offrom about 5 to about 10% by weight.

The weight ratio of ammonium nitrate to nitromethane is a criticalfeature of the present invention and, as previously stated, must be inthe range of from about 65:35 to about 45:55. Preferably the weightratio of ammonium nitrate to nitromethane is about 60:40.

The particle size of the ammonium nitrate is also a critical feature ofthe present invention and, as previously stated, the ammonium nitratemust be of particle size sufficient to substantially completely passthrough a 10 mesh screen with not more than 22% by weight passingthrough a 200 mesh screen. The particle size distribution is preferablyas follows:

Screen Size Percentage (U.S. Sieve Series) Minimum Maximum +10 0 0 10+350 10 -35+60 O 40 60+100 0 30 +200 10 22 200+Pan 15 22 for ammoniumnitrate are well known to the art and include diatomaceous earth, wax,kaolin clay and the like.

The explosive compositions of the present invention are readily preparedby forming an intimate admixture of ammonium nitrate, nitromethane andgelling agent in the amounts and ratios set forth above. The mixing maybe carried out by any suitable procedure using mixing equipment suitablefor mixing the ingredients. The intimate admixtures have the consistencyof heavy doughs and may be termed gels. The compositions may be formedby first mixing the nitromethane and gelling agent to form a thickenedor gelled nitromethane composition and subsequently mixing the gelledcomposition with the ammonium nitrate. As an alternate procedure, theammonium nitrate, nitromethane and gelling agent may be placed in mixingequipment and mixed in a one-step operation.

By way of example, 600 lbs. of ground ammonium nitrate of particle sizesufficiently small to substantially completely pass through a meshscreen with not more than 22% passing through a 200 mesh screen preparedby grinding fertilizer grade, high density, ammonium nitrate prills, 400lbs. of nitromethane and lbs. of nitrocellulose are placed in a mixingmachine and the mixer is operated until an intimate admixture is formed.After thorough mixing the admixture may be packaged in desiredquantities. By way of example, the mixture is passed to a hopper andthere fed in 50 lb. quantities or other quantities into appropriatelysized water resistant containers. The loaded container is then equippedwith a detonating device, as for example, a primer, of sufiieient powerto detonate the explosive composition contained therein. The containerscan be formed of any suitable container material. Waterproof or waterresistant containers are naturally preferred. Typical containermaterials include polyethylene, polyvinyl chloride, polystyrene, fibrousmaterials such as wood, paper and cardboard; ferrous metals andnon-ferrous metals such as tin, copper and aluminum. The packagedexplosive composition is suitable for detonation under water in theseismic exploration for oil and natural gas. The packaged explosivecomposition has a detonation rate of in excess of 18,000 feet per secondand is non-cap-sensitive.

From the foregoing those skilled in the art should readily understandthat the present invention provides explosive compositions which arewell adapted for uses requiring non-cap-sensitive gelled explosivecompositions having high rates of detonation.

Since many embodiments of this invention may be made and since manychanges may be made in the embodiments described, the foregoing is to beinterpreted as illustrative only and the invention is defined by theclaims appended hereto.

1 claim:

1. A non-cap-sensitive explosive composition in gelled form having ahigh detonation rate consisting essentially of an intimate admixture ofammonium nitrate of particle size sufiiciently small to substantiallycompletely pass through a 10 mesh screen, not more than 22% by weight ofsaid ammonium nitrate passing a 200 mesh screen, nitromethane andgelling agent for the nitromethane, the weight ratio of ammonium nitrateto nitromethane being in the range of from about :35 to about 45:55, andthe amount of gelling agent being sufiicient to effectively thicken saidmixture.

2. The composition of claim 1 wherein the weight ratio of ammoniumnitrate to nitromethane is about 60:40.

3. The composition of claim 1 wherein the amount of gelling agent is inthe range of from about 2 to about 15% by weight based on the weight ofthe nitromethane.

4. The composition of claim 1 wherein the amount of gelling agent is inthe range of from about 5 to about 10% by weight based on the weight ofthe nitromethane.

5. The composition of claim 1 wherein the gelling agent isnitrocellulose.

6. The composition of claim 1 wherein the ammonium nitrate is ofparticle size distribution to be partially retained on screens 35, 60and mesh.

References Cited UNITED STATES PATENTS 1,113,275 10/1914 Woodbury149-1l2 X 3,133,844 5/1964 Royer et al. 149-89 X 3,255,057 6/1966 Broweret al. l49-2 3,318,741 5/1967 Jones 149-89 CARL D. QUARFORTH, PrimaryExaminer. L. DEWAYNE RUTLEDGE, Examiner. S. J. LECHERT, JR., AssistantExaminer.

